Peel and core apples. Finely chop half of one apple and cut the rest into 12 wedges. Toss the apple in lemon juice.
Heat half the butter in large frying pan. Add the chicken pieces, skin side down, and cook until golden. Turn chicken over and cook another 5 minutes. Remove the chicken and pour off fat.
Heat 1 tablespoon butter in the same pan and add onion, celery and chopped apple. Fry over moderate heat for 5 minutes without browning.
Remove from heat. Sprinkle flour into mixture and stir. Add Calvados and return to heat. Gradually stir in cider. Bring to a boil, return chicken to pan, cover and simmer gently for 15 minutes.
Heat remaining butter in small frying pan. Add apple wedges and fry over moderate heat until browned and tender. Remove from heat and keep warm.
Remove the chicken pieces from the pan to a platter and keep warm. Skim excess fat from cooking liquid. Add creme fraiche, bring just to a boil and simmer 4 minutes, until it thickens enough to coat the back of a wooden spoon. Season with salt and pepper. Pour sauce over chicken and serve with warm apple wedges.